1. Field of the Invention
The present invention relates to a method for transmitting a digital channel with priority of a mobile communication terminal, and more particularly, to a method for transmitting a digital channel with priority of a mobile communication terminal capable of searching/transmitting a digital channel with priority which is available for service in an analog field area.
2. Description of the Background Art
In general, a field environment of a mobile communication terminal is divided into an analog field and a digital field. In order to resolve the shortcomings such as a limited capacity and low service quality and performance of an analog system implemented in the analog field, a digital system implemented in the digital field is increasingly used.
Because much time and high cost are required to construct a service network for implementing the digital system, an improvement is made such that a digital cellular phone service can be provided on the basis of an Advanced Mobile Phone Service (AMPS), the analog field and the digital field co-exist in some area.
The AMPS is a typical example of the analog system which provides an analog cellular phone service by using a frequency division multiple access (FDMA) method, is operated at a frequency band of 800˜900 MHz and each channel has a 30 KHz band width.
FIG. 1 is a block diagram of a construction of a general mobile communication system.
When a mobile communication terminal 10 is registered for a base station 20, the base station 20 provides various system parameters, a system identification (SID) and a network identification (NID) to the mobile communication system 10. The mobile communication terminal 10 determines a system for receiving a service through a series of processes, and originates or receives a call according to user's selection.
The mobile communication terminal determines the system by using an acquisition record table and a system record table, which are called a preferred roaming list (PRL). The acquisition record table includes an analog/digital mode information, frequency information and a band class information, while the system record table subordinated to the acquisition record table includes SID/NID information, preferred or negative information, a priority or a roaming indicator.
The mobile communication terminal includes a most recently used (MRU) table storing certain channel information used for recently determining a system among information of the acquisition record table.
FIG. 2 is a flow chart of a general system determining method of a mobile communication terminal.
The mobile communication terminal sequentially stores every channel information read from the MRU table in a scan list (step S11), stores every channel information read from the acquisition record table (step S12), and sequentially scans the scan list to try to obtain a service available system.
In this case, the scan list includes only channel information, not SID nor NID.
The mobile communication terminal compares a parameter of the obtained system and information stored in the system record table (step S14). If the corresponding system parameter indicates that the obtained system can be available for service in the system record table, the mobile communication terminal determines it (step S15).
The mobile communication terminal, which is idle in the analog field, performs a searching in order to obtain a digital system every second minutes. At this time, the mobile communication terminal scans a channel to search the strongest signal and then is maintained in the idle state in a system mode of the corresponding channel.
In the conventional art, when the mobile communication terminal in the analog mode originates a call in the analog field, the call originating is performed in the currently obtained analog mode.
Thus, in the case that the call originating is performed in the analog field, a call should be made through an analog channel, causing a problem that a speech quality is degraded.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.